Store round start date in the database (#21153)

Content.Server.Database/Model.cs

@@ -111,6 +111,13 @@ namespace Content.Server.Database
                 .HasForeignKey(player => player.PlayerUserId)
                 .HasPrincipalKey(player => player.UserId);
 
+            modelBuilder.Entity<Round>()
+                .HasIndex(round => round.StartDate);
+
+            modelBuilder.Entity<Round>()
+                .Property(round => round.StartDate)
+                .HasDefaultValue(default(DateTime));
+
             modelBuilder.Entity<AdminLogPlayer>()
                 .HasKey(logPlayer => new {logPlayer.PlayerUserId, logPlayer.LogId, logPlayer.RoundId});
 
@@ -468,6 +475,8 @@ namespace Content.Server.Database
         [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
         public int Id { get; set; }
 
+        public DateTime StartDate { get; set; }
+
         public List<Player> Players { get; set; } = default!;
 
         public List<AdminLog> AdminLogs { get; set; } = default!;